R e v i e w s

Physics of nuclei and elementary particles

Moscow University Physics Bulletin 2020. N 3.

The properties of giant dipole resonance (GDR) of a large group of light atomic nuclei are analyzed. The analysis is based on the systematics of photoabsorption cross sections for the 31 nuclei with the number of nucleons from 12 to 65, created from experimental data available in the scientific literature. In cross sections included in the systematics, such effects as configurational and isospin splitting of the GDR are clearly manifested. These cross sections are recommended for testing modern theories of the GDR.

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Astronomy, astrophysics, and cosmology

Moscow University Physics Bulletin 2020. N 3.

In this paper, we exactly solve the Wheeler-DeWitt equation in the presence of a conformally coupled scalar field and in the context of the generalized uncertainty principle (GUP). The GUP-corrected Wheeler-De Witt equation in momentum space leads us to introduce factorization method. This method helps us to obtain the exact solution for the corresponding system. So, here we factorize the second-order equation in terms of first-order operators. These first-order operators help us to arrange partner potential and superpotential. Also, we achieve the general quantum stats and energy spectrum for GUP with conformally coupled scalar field system. Also, we show that the stability of a system with the energy spectrum with some conditions.

Show AbstractPhysics of nuclei and elementary particles

Moscow University Physics Bulletin 2020. N 3.

In this study, we compare the direct and indirect parametric reconstruction approaches (4D and 3D respectively) in terms of their performance in terms of kinetic parameter estimation, and a noise measurement represented by the normalized standard deviation. A numerical phantom with simple geometric shapes has was modelized to evaluate these performances on several sizes of spheres.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

The spin response of the $\vec\gamma\vec d\to\pi^0d$ reaction near threshold is investigated. Our formalism based on the impulse approximation, uses the realistic Bonn $NN$ potential (full model) for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary $\gamma N\to\pi N$ amplitude. We present the first results for the double polarized differential and total cross sections for parallel and antiparallel helicity states, the deuteron spin asymmetry, the helicity $E$-asymmetry, the deuteron GDH integral, and the double spin asymmetries of the total cross section in the near-threshold region. Sensitivity of the estimated results to the $D$-wave effect of the deuteron wave function for a realistic $NN$ potential is studied. We find an insignificant sensitivity of most of the estimated observables to the $D$-wave component. A noticeable role is obtained only in the double polarized differential cross section with antiparallel spins of photon and deuteron $d\sigma^A/d\Omega_\pi$ close to the threshold energy at forward and backward pion angles as well as in the double spin asymmetry of the total cross section $\sigma\Tilde T_{20}$ at relatively large photon energies. Thus, we compare results for these two observables using various $NN$ potential models with different $D$-state probabilities, and a noticeable influence is found.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

Collisions of metastable antiprotonic helium atoms with atoms of the medium cause, among other processes, transitions between hyperfine structure (HFS) states, as well as shifts and broadening of microwave M1 spectral lines. In order to obtain interaction potential matrix ($\bar{p}$ He$^{+} - He), the potential energy surface (PES) is calculated in the unrestricted Hartree-Fock method taking into account electron correlations within the second-order perturbation theory (MP2). With this potential, the system of equations of close coupling of HFS channels is numerically solved, and cross sections and transition rates, shifts and broadening of M1 spectral lines are calculated, which are then used to solve the kinetic equation that determines the time evolution of the HFS-states density matrix. The results are compared with experimental data and with model calculation results.

Show AbstractBiophysics and medical physics

Moscow University Physics Bulletin 2020. N 3.

This study aims to calculate the air Kerma to personal dose equivalent conversion coefficients Hp(0.07) for mono-energetic photons from 0.015 to 10 MeV for angles of incidence from 0° to a 75° in steps of 15° using Mont Carlo (MC). In addition to this, we propose a new equation to perform an analytical fit of our Monte Carlo calculated conversion coefficients for photons. Hp(0.07)/Kair values have been determined by two terms: in term of absorbed dose, according to the definition of this quantity, and also with the term of Kerma approximation. The results obtained are compared to those published in Joint report of ICRU and ICRP, 2017, 2017. A good agreement with reference data with a local difference less than 2 % was observed.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2020. N 3.

An effective Lagrangian is obtained and a group of hidden symmetries is found for Maxwell’s theory with an axion in stationary case. A general harmonic solution of the problem is constructed; it is shown that a central source can only have a Coulomb-type magnetic field. The electric field of such a source has a complex potential, which can be finite everywhere with a special choice of parameters. The differential scattering cross section of the test particle on a dione with an axionic charge is calculated in the first order of the perturbation theory.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2020. N 3.

Single-crystal silicon was irradiated with xenon ions with energies of 100, 200 keV and argon ions with an energy of 110 keV. The irradiation fluence varied in the range of the parameter “displacement per atom” (dpa) from 0.1 to 1 for both types of ions and selected energies. The effect of irradiation on the damaging of the silicon structure was studied by the methods of Rutherford backscattering in combination with channeling and Raman scattering. The stages of destruction of the crystal structure of silicon on the basis of Rutherford backscattering spectroscopy and Raman scattering for different irradiation fluences are demonstrated. It was shown that with increasing fluence to a value corresponding to the value of 0.5 dpa, defects accumulate in the modified layer and then highly defective regions merge into amorphous layers. At the dpa value of 1, complete disordering of the single crystal structure is not observed.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

The results of the gold deposition into the pores of SiO$_2$/Si matrices, as well as modifications of the obtained SiO$_2$(Au)/Si systems due to irradiation with argon ions of Ar + with an energy of 100 keV and a fluence of 5×10$^{14}$ ion/cm2 are presented in this work. The effect of irradiation on the surface topography change of SiO$_2$(Au)/Si systems and the intensity of the SERS signal during the detection of the test analyte Methylene Blue is demonstrated.

Show AbstractCondensed matter physics

Moscow University Physics Bulletin 2020. N 3.

Within the framework of the coherent potential approximation for the s-d model, taking into account the electron-phonon interaction, the electrical resistivity ρ, and Hall coefficient R$_0$ of disordered paramagnetic Au$_x$Pd$^{1-x}$ alloys are calculated. On the example of these alloys mechanisms responsible for correlation between resistivity and its temperature coefficient (Mooij rule), and correlation between temperature dependencies of ρ and Rо are discussed. The obtained results are in good agreement with experimental data.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

The field dependences of the magnetization of nitrogen-containing compounds R(Fe,Ti)$^{12}$N (R = Ho and Er) are analyzed. It was found that the initial HoFe$^{11}$Ti sample at T = 4.2 K exhibits an easy axis type anisotropy; however, as a result of nitriding, the anisotropy type changes to the cone of the easy magnetization axes. In HoFe$^{11}$TiN and ErFe$^{11}$TiN nitrides, as well as in the initial HoFe$^{11}$Ti and ErFe$^{11}$Ti samples, a cascade of spin-reorientation phase transitions induced by an external magnetic field is observed. In the framework of molecular field theory, the effect of nitriding on interlattice exchange interactions is estimated. It has been established that the molecular field acting from iron sublattice on rare-earth ions (holmium and erbium) is enhanced. The effect of nitriding and hydrogenation on the interlattice exchange is compared.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

Thermally Stimulated Depolarization Currents (TSDC) of Triglycine Sulfate (TGS) single crystals pure, γ-irradiated and doped with Cr3+ ions – were studied. When thousandths of a weight percent of interstitial impurities (Cr, Cu, Fe) are introduced into the lattice of TGS single crystal at the stage of growth, the domain structure stabilizes (monodomainization), the region of the polar phase expands (up to TM≈110°C), but the analogy of the dielectric response at the Curie point TC≈49.7°C is preserved. These effects are observed on the TSDC curves as a peak around TC and additional diffuse anomalies around TM. Similar phenomena take place in TGS crystals irradiated with γ-rays in the presence of a polarizing constant electric field. These anomalies are probably due to changes in the energy of protons at their jumps to a higher energy level in the double-well potential of a hydrogen bond.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

An analytical expression describing the space-time distribution of the thermal field in a crystal irradiated with synchrotron x-ray radiation with an arbitrary space-time structure is found.

Show AbstractMoscow University Physics Bulletin 2020. N 3.

The paper presents the results of the melting and study of the magnetostrictive properties of the multicomponent Sm$_{0.2}$(Y,Tb)$_{0.8}$Fe$_2$ alloys. In this system, by varying the component concentration, temperature, and an external magnetic field, one can influence competing exchange interactions and observe a number of unique phenomena, such as magnetic compensation. By using X-ray diffraction analysis it was found that the alloys have a cubic crystall structure of the C15 Laves phase. Longitudinal and transverse magnetostrictions were studied in the temperature range from 80 to 300 K in magnetic fields up to 12 kOe. Using their values, volume and anisotropic magnetostrictions were calculated. An inversion of the sign of the volume magnetostriction at T = 150 K was found in Sm$_{0.2}$(Y,Tb)$_{0.8}$Fe$_2$ compound. It is shown that the volume magnetostriction of a number of alloys does nearly unchanged with temperature and is close to zero value in the temperature range 150-300 K. The results are discussed in the frame of a three magnetic sublattice model with competing exchange interactions.

Show AbstractEngineering physics

Moscow University Physics Bulletin 2020. N 3.

A measuring complex for recording events by single-photon superconducting detectors based on NbN structures is presented, in which low-noise, high-frequency HEMT transistors are used as cryogenic amplifiers.

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